How to configure ADC frecuency? Freescale K70

Hi, i am trying to configure the ADC Module from Freescale K70 TWR MK70FN1M0VMJ12 using Processor Expert for a simple audio processing, but in conversion time i can't set 44Khz sampling for example. I can only choose between a set of possible values of clock. How can i accurate the sampling frecuency to an particular value using PE?